The present invention relates to a method for monitoring or measuring the uniformity of tows with mechanical sensing elements in the course of production on a tow line.
In the production of synthetic fibers it is necessary to confer the desired textile properties on the spun filaments in a number of aftertreatment steps. Examples of aftertreatment steps which are generally necessary are drawing, setting, crimping and, where appropriate, cutting the continuous filaments into staple fibers. These aftertreatment steps are in general carried out in industry on tow lines by first combining the filaments from a plurality of spinnerets to form a tow which is then deposited in cans and then combining a plurality of these tows and subjecting them together on a tow line to the abovementioned aftertreatment steps of drawing, setting, crimping, etc. The tows aftertreated at the same time in this manner contain a very large number, generally from several hundred thousand to several million, individual filaments.
Especially tows which are subsequently to be further processed as converter tows, stretch-breaking tows or filling fiber tows must be of uniform quality and comprise in particular a constant number of filaments. Any change in the thickness of a tow leads to nonuniformity and hence a quality defect in the end product.
For technical reasons, for example because the canned tows of freshly spun filaments are not infinitely long, imperfections due to the running out of supply cans and the then necessary recruitment of replacement tows are unavoidable. Similarly, spinning-out problems which can lead to the breakage of individual filaments and to clumping and blob formation produce hard places in the tow and reduce the quality thereof. It is therefore necessary to monitor the tows for irregularities in order that the proportion of end product which is of inferior quality due to the presence of an irregularity may be eliminated from the production process. The tows are usually monitored visually by the operating personnel. In specific areas it is also already possible to use automatic equipment which is supposed to minimize the effects of tow irregularities on the end product.
Apparatus for this purpose is known for example from German Auslegeschrift 2,144,104, German Offenlegungsschrift 2,400,293 and German Patent No. 11,208. The apparatus known from German Auslegeschrift 2,144,104, and German Offenlegungsschrift 2,400,293 comprises sensing rollers which sense the thickness of the tow. In the apparatus of German Patent 11,208 this function is performed by a so-called sensing saddle, which is intended to be thrown upward by thick places in the tow.
German Offenlegungsschrift 3,306,687 describes an apparatus for bringing together a plurality of synthetic fiber tows upstream of a crimping box by means of pivotable deflecting rolls, said apparatus comprising tow tension measuring and control units. The tow tension is measured here only to provide automatic control of the deflecting rolls, so that the bringing together of the tows can be optimized. The apparatus does not have the purpose of detecting the quality of the tows.